Treatment of household drinking water by passing the water through a bed of activated charcoal impregnated with or having oligodynamic silver or other bactericide adsorbed thereon is known from the prior art. For example, U.S. Pat. No. 2,595,290, patented May 6, 1952, U.S. Pat. No. 3,242,073 patented Mar. 22, 1966, U.S. Pat. No. 3,268,444, patented Aug. 27, 1968, U.S. Pat. No. 3,585,130, patented June 15, 1971, and the references cited therein.
In addition to the above cited patented prior art, the United States National Aeronautics and Space Administration (NASA) has conducted experiments (see first paragraph below) and constructed apparatus for treating spacecraft water with silver ions for biocidal and virucidal purposes (see second and third paragraphs below).
The first NASA reference is entitled "Biocidal Effects of Silver, Contract NAS 9-9300. Final Technical Report, February 1971. Dean O. Cliver, Ph.D, University of Wisconsin." This study reports on the biocidal virucidal effects of silver ions in a very pure distilled or deionized water, and the bacteria involved are not pathogens as found in natural water. This study indicated that increased silver ion levels reduce kill time and the inhibitory effect of chlorides is mentioned. However, there is nothing in this report regarding techniques for introducing silver ions into natural water utilizing silver salt and silver metal adsorbed and impregnated in activated charcoal to obtain high silver release at seasonal customary water temperatures in accordance with the present invention.
A second NASA reference is entitled "Potable Water Bactericide Agent Development. Contract NAS 9-912104. Final Report 3097, July 1972; Chemtric Inc."
The report deals with the development of a silver ion purification system designed to treat "worstcase" water produced as a by-product of fuel cells to be used in the Orbiter program. A specific water analysis was involved. For various reasons, a specific sequence of units was established.
A. Biological Filter containing AgCl particles.
Filter was designed to remove particulates and biological contaminants that would otherwise rapidly clog the ensuing system.
B. Activated Carbon Filter.
A plain activated charcoal filter was used to remove add taste, odors, colors, and other impurities not removed by the Biological filter.
C. Silver Chloride Column.
A column composed of crystals of silver chloride interspersed among glass beads was used to dose the water with silver ions. At natural concentrations of 1.35.times.10.sup.-3 g/l, the silver ion content would be far in excess of that reported by Cliver.
D. Water Storage Tank.
A pair of water storage tanks was next in the series. No apparent reasons were given for location of the tanks at this point in the sequence. Obviously, the supply flow rate of approximately one gallon per hour required an intermediate storage point in order to deliver product water at approximately 7 gallons per hour. It is worth noting that two tanks (of unstated size) were used--connected in parallel, rather than in series. Further, however, the system could bypass the tanks entirely, thus implying a lack of concern with holding time to allow complete biocidal effect.
E. Deionizer.
A deionizing column was inserted to remove silver ions, since the level was in excess of the permissible 50 ppb. Apparently no other means was considered for silver removal. The disadvantages of de-ionized water were considered to be outweighed by the need for a potable water.
F. Silver Bromide Column.
It was recognized that the de-ionized water (with near 0 silver content) was susceptible to further biological contamination prior to use. Therefore, it was considered necessary to add additional silver--within the 50 ppb limit--to the water as a final process stage. A temperature gradient chart was provided that indicated the silver bromide crystals would release in the 50 ppb range when the water was at normal room temperatures. However, when water temperature increases, silver ions are released at an increasing rate. Insofar as the Chemtric report is concerned, the temperature effect was related solely to water temperature.
In summary, the report deals with a specific situation, and inserts units into a system to deal with a specific condition. At no time is the broad problem of natural water considered.
The third NASA reference is entitled "Advanced Prototype Silver Ion Water Bactericide System. Contract NAS 9-13718, Final Report 3104, Dec. 1974, Chemtric, Inc." The report deals with a greatly modified system designed to treat water produced by the fuel cell selected for the Orbiter Program.
The water quality of the selected fuel cell's output is considerably improved over the "worstcase" reported on in Report No. 3097. Therefore, the system consists of a single outer container with a small inner container. The active function of the unit is twofold:
A. A "roughing" or prefilter designed to remove all particulate matter and organisms in excess of 0.35 microns, and 98% of particulates as small as 0.15 microns.
B. A mixed column of Activated Carbon (80%) and Silver Bromide granules (20%) designed to adsorb small quantities of organics, and to release between 40 and 85 "ppb" of silver ions to the filtrate.
The report includes a repeat of the water temperature-silver ion release phenomenon. The solution selected is to insert a heat exchanger between the fuel cell collection tank and the purification unit. In other words, to control the water temperature as a control over silver emission.
No new data was presented in the report.
In none of the above identified patents or reports is the problem of chlorides in water inhibiting the ability of a silver salt adsorbed and impregnated on activated carbon to release silver ions.
The prior art of natural water treatment methods and apparatus fails to provide for the fact that chlorides in natural water will combine with silver ions to form either a silver chloride precipitate which does not appear to be as effective as a biocide as silver ions, or the chlorides limit the solubility of silver ions from silver salts and metallic silver impregnated and adsorbed on an activated carbon media. Further, the prior art teaching has been to alter the silver-activated charcoal media to achieve the desired silver release for biocidal purposes, whereas, according to this invention, the water is altered to allow the silver-activated charcoal media to achieve its designed objective.
The treatment of water by oxidizing disinfectants such as chlorine is well known. However, it has recently been shown that the action of chlorine on organic materials in water will produce halogenated organics with suspected carcinogenic properties. These organics include the trihalomethanes such as chloroform and bromoform. Efforts to reduce the formation of halogenated organics in water have included changing the point of chlorination in the water treatment process or replacing chlorine by another disinfectant such as ozone. As a stronger oxidizing agent than chlorine, ozone can oxidize halide ions to the halogen form resulting in the formation of halogenated organics. Other oxidizing agents used in the practice of this invention also product halogenated such as trihalomethanes. To avoid the production of halogenated organics from an oxidizing disinfectant, the halide ions are removed from the water in a initial treatment station. If the halides are replaced by another anion, i.e., bicarbonate, the original ionic concentration of the water is maintained, thereby essentially maintaining the natural character of the water, a natural buffer is added to the water and the bicarbonate will not be affected by any known oxidizing disinfecting agent. Thus, it is shown that halide removal is required before disinfection with silver to avoid precipitation of silver halides and also before disinfection with strong oxidizing agents to prevent formation of halogenated organics.